The present invention relates to pressure regulators for hydraulically controlled machine tools.
Use of devices actuated by a pressure medium in machine tools, for example, for hydraulic clamping cylinders, hydraulic tailstock sleeves and steady rests requires maintenance of a certain work pressure throughout the entire machining time in order to ensure safe clamping of the workpiece. On the other hand, the certain work pressure should not be exceeded as this could result in damage to the chucks or the workpiece.
In hitherto known machine tools, the work pressures are set by pressure-regulating valves with directly controlled spools which enable regulation of a settable work pressure and must be adjusted manually. Therefore, a pressure-regulating valve is provided for each work pressure and, as a result, up to four pressure-regulating valves must be adjusted by hand prior to a machining operation.
Pressure regulators which are adjustable by a machine control system are known, but these are pilot operated valves and seat valves which are not suitable for use in machine tools as they are sensitive to vibration and dirt and are thus susceptible to failure. For example, a chip under the conical or spherical sealing seat of a pilot operated valve changes the set pressure in an uncontrolled manner in the downward direction, with the result that the above-mentioned work pressure can no longer be maintained. Therefore, on account of their low susceptibility to failure, only pressure regulators with a directly controlled spool can be used in machine tools.
Use of proportional magnets to adjust pressure regulators is also known. This is similarly not suitable for machine tools as the set work pressure must be maintained in the event of a power failure, otherwise the workpiece would come loose from the chuck or in the event of too high pressure, the chuck, its jaws or even the workpiece would be overstressed.
Thus, directly controlled pressure regulators are the only ones usable for machine tools, but have the disadvantage that the work pressure, which is set manually, is dependent upon the meticulousness of the operator. Also, the time required for setting in machines with otherwise short set-up times, for example, in numerically controlled machine tools, is excessive.
The object underlying the present invention is, therefore, to provide a pressure regulator with which the required work pressure can be set by a machine control system.